import PySimpleGUI as sg

sg.theme('Default1')

layout = [
    [sg.Text('请选择主题')],
    [sg.Listbox(values=sg.theme_list(), size=(30, 10), key='-LIST-', enable_events=True)],
    [sg.Button('Exit')]
]

win = sg.Window('theme列表', layout, alpha_channel=.9, grab_anywhere=True)

while True:
    event, values = win.read()
    if event in (sg.WIN_CLOSED, 'Exit'):
        break
    print(values)
    select_values = values['-LIST-'][0]
    print(f'select values: {select_values}')

    sg.theme(select_values)
    sg.popup_get_text('选择了新主题{}'.format(select_values))

win.close()